If you are connected via a hose to your city water connection ALL plumbing lines in the system are pressurized even right up to pump discharge and fill valve to fresh water tank if you have one on water panel.
So.......no place to suck air into that pressurized system.
If there was an 'air' source it would leak water check valve in pump---water would leak back into fresh water tank, fill valve---water would leak back into fresh water tank, any other fitting etc---water would leak out)
Think you just have some trapped air in system from recent disinfecting.
